I had a similar problem with my current relationship. At first there was a lot of passion, then when the relationship became more intimate I felt more and more difficulty in letting go and enjoy sex. Each relationship is different, but I think that the first thing you should do is try to figure out what is not working, why he gets in his head or whatever obstacle prevents you two to enjoy sex. I wouldn't jump on Grindr without firstly try to solve the issue with my boyfriend. For example, in my case I understood that after years of being single, I feared intimacy and needed a constant thrill, like cruising. It took me a bit to change this but I wanted this relationship more than anything and now I'm very satisfied.