I'm a recent law school grad, my primary partner is an accountant. Our professional lives take over at times (most recently bc of tax season), and our intimacy suffers as a result. To combat the feeling of distancing, we write letters to each other about daily life, our relationship. I prefer 'verbal' affirmation (i.e. words) anyway, so letter-writing makes me feel very reassured and cared for. That seems to work for us, so it's a suggestion. Although I don't know if that would work for you or your partner.

You wrote that you feel like "closeness had gone" bc of work, that the level of contact/intimacy you have now is not cutting it for you. Does your partner feel the same way? Maybe your partner feels quite content with the level of contact in your relationship. I like creating conversation Qs before my partner and I meetup. In your shoes, I might consider asking myself and my partner: How do I/you prefer to sustain intimacy? (perhaps more daily contact by phone, text, FaceTime?) And when I feel like something is off about a relationship and wanna talk about it, I'll say something like "Hey, I wanted to check-in and see how you were feeling about the way we've been relating to one another lately. How are things going for you?" I find this tends to open up discussion well.

As for finding it difficult to get your partner to open up, that is challenging; especially since you've both already talked about the issue. I also find it really unpleasant to be the one to almost always initiate conversation, dates, physical touch because it makes me feel undesirable, unattractive, clingy. Have you told your partner about how this pattern of behavior is making you feel? And if so, has your partner offered to do a little more heavy-lifting in the relationship w/re. to communication?

Another thing to consider, re. "It's difficult to get my partner to open up." -- As much as you may wish it and want it, you can't make anyone do anything. Our partners show up, and the extent to which they can or want to be available, open, giving is wholly up to them. You can certainly communicate that you want more, but ultimately, it's out of your hands. I think taking some space is a great idea because it sounds like an amazing opportunity for you and your partner to reflect on what each person wants and needs in order to keep your long (and presumably healthy) relationship going.

It's really hard to know when a relationship is over-over because there are so many factors to consider. Although, in my experience, almost all of my relationships ended because someone's feelings (and subsequently their level of interest) changed. And that's just a thing that happens. Barring cheating or other drama, changing feelings are no one's fault.