I'm so sorry that sex has been painful for you. From what we know, painful intercourse isn't something that simply goes away if you give it enough time. True, if a lot of it is coming from anxiety or nerves at doing something new, that may indeed get better with time. But, in your case, it sounds like there may be some other causes that need addressing. For starters, how much lube has been used the times you've tried this? And, did you get support after the assaults, including support for ways trauma from those incidents might pop up places you don't want it to?
It's great that your boyfriend is being understanding! Since it sounds like he's a respectful partner, how would you feel about setting a boundary with him that you two don't have vaginal intercourse for awhile? If you're dreading it and it's causing you pain, you get to set the limit of only doing other sexual things with him (if you want) . Continuing to do it when it hurts is only going to reinforce the dread or tension, which in turn is going to make it more likely that pain happens.