So this is my first time chiming in on this subreddit, I've only lurked.
I'm also an engineer who travels a lot for work (spent 144 days away from home last year), and it's definitely tough, but my girlfriend and I make it work.
Firstly, you should let your boyfriend know that this is what he signed up for. You are an engineer, a young professional trying to gain a foothold in your career. There will be more travel down the road, and at this stage in your career you can't really say no, he needs to accept that. As an engineer, you'll be working with primarily male co-workers, and that's something he needs to accept as well. I see lots of people saying to break up with him, but I think you should at least give him some time to try to accept these facts, assuming your relationship is otherwise going well. Reassure him that he is your boyfriend, he is the one that you choose to be with, and he needs to be secure about that fact for things to work. If you're at the stage where you say you love each other, tell him you love him. Maybe joke about how engineers are a bunch of weirdos anyway, and he's got nothing to worry about.
With facebook messenger, skype, facetime, et cetera, there are plenty of ways for you guys to keep in touch without cell phone service, and there's plenty of free wifi around these days. Even when I'm really busy, my girlfriend and I will at least have a little "how was your day", or "goodnight, I love you", or "I miss you".
There are silver linings too. The forced time apart gives you each some "me time", which is nice. Me personally, I bring my PS4 to my hotel and get all my video gaming out of my system while I travel haha. It's nice to have that "me time", get that out of my system, and when I'm home I put down the video games and spend time with my girlfriend. If he has other hobbies that he has trouble finding time for, your travel is a perfect time for him to get back into them. Also, if you get per diems while travelling, I like to live cheap while I travel, buy groceries and premade sandwhiches at grocery stores/delis and stock up my hotel mini fridge, then pocket a bunch of my per diems. Then when I get home I take my girflriend out for a nice dinner and drinks "courtesy of my unspent per diems". The frequent flyer miles and hotel loyalty points can also add up pretty quick, it's nice to go on a vacation on points you've racked up from work trips!