Hey, so I hope my previous comment was helpful. After coming back to your post, I realized that even if it works, it will only get you to the point where your bf (hopefully) agrees to address the issue with you. You still may have NO idea how to fix it! I have some suggestions, and I'll tell you what worked very well for me. Now, apologies, but I already had most of this (long) reply typed out and then hit the back button on my mouse and it was deleted, I might make it a bit more concise here as I'm running out of time.
So, he (hopefully) says "okay, let's work on this together" or something like that. Yay!!! Now what?
First, I suggest you get a little notebook, nothing special, and a pen. Sit down together and make a list of things you want to change about your relationship. State them as what you want to achieve (i.e. more frequent sex, which you can make even more specific as sex x times per week). If that's the only thing on your list, great, but you may have more. For me it was not just frequency of sex but quality, particularly certain acts of foreplay that were essentially non existent.
Okay, now you have a list of what needs to be addressed. The list should have a DATE on it. This is so you know when you started working on this. Give yourself a deadline for when you want to reevaluate your relationship (I gave myself 6 months) and I personally did not tell my boyfriend about the deadline. He doesn't need that pressure. It's just for me, cause unsatisfying relationships can not be an indefinite thing, and we all know that some people just don't change. The deadline doesn't have to mean the problem is solved by then, just that you are going to revisit your progress and see if it's enough for you.
Now, you have a list of what you need to work on. Move on to your second list. The second list is actions you are going to take, i.e. things you are actively going to do to bring about the changes you want. Whether it be initiate sex more, be more flirty/provocative, etc. Again, be specific. If he is going to initiate more, don't write down "initiate more". Write Initiate x times per week or at what time of day or different specific ways he can try. Be realistic about what you think will and won't work for you. Your bf needs to step up here and say what he can do to make this work for you, but he also needs to be honest and tell you what you can do for him to help him change. You are both working together making changes here, like a partnership.
By the end of this talk you should have penned down exactly what you are going to do differently to make sex happen more often. Now go about your merry lives, making a conscious effort to do these things. Have a goal to talk about this again in 1-2 weeks.
Okay, 1-2 weeks later. Sit down with your notebook. By the way, make sure you are having these talks when both people are relaxed, have energy, and are open to working on things. Do not do it when tired, stressed, angry, hungry, etc. Positive state of mind only!! Anyway, sit down, look at your "to do" list from last week and see how you did at attempting these things. Did you actually make an effort? What worked? What didn't? Don't expect things to work 100%, sometimes you only have a small success, or you don't but still think it might. Change takes time. You likely learned things that give you new ideas for stuff to try, so add and revise your "to do" list as you go.
Keep meeting regularly, 1-2 weeks is what I suggest. Revise your "to do" list as you go (just so we're clear, this is the list of things you're working on to make your relationship meet your needs / address your "deal breakers")
One thing that worked for us on our "to do" list was sex scheduling. we decided on twice per week, which was more frequently than it was currently happening but not as much as I wanted (we were working up to that). We picked the days and realized quickly on that it's a bad idea to leave it right to the end of the day when everyone's tired. It needs to be prioritized.
Another thing that worked for us was trying different ways and times of day to initiate sex. Before bed usually wasn't successful (too tired) so we tried more during the day. Initiating in ways that were more flirty/fun.
The other things on our "to do" list were more specific to us, and not so much about frequency, so they may not help you and I'll leave them out.
Other things that may help is that I found it helpful to try to take a "solution focused" approach when you are unhappy about things. "You never initiate" focuses on the problem and should be avoided, whereas "It would help if you initiate more" focuses on the solution and is more positive. For every problem there is a solution, and you tend to go where you focus in life, so focus on the solution.
Last thoughts... you can't make someone change. You may notice your partner is not trying to make the changes you both agreed upon and just not putting in the effort. You can talk to him and work with him to work harder and put in more effort, and hopefully he will improve, but there is a possibility he won't. I am lucky to have a partner willing to work on things with me and make changes to help meet my needs. If I ever again find myself in a relationship with a guy who does not make an effort to change to help meet my needs, I will walk away. That kind of person is not life partner material. In my current relationship we are now in the habit of both voicing things that are not working for us and together coming up with a solution. We both work to change to help the other person be happy and satisfied. To me that is how a relationship should work. If a partner is not willing to change, they are essentially saying "I don't care if this isn't working for you. Just deal with it" and I would deal with that by finding a new partner.
This was insanely long, but I hope it is at least a little helpful. Good luck!