Sex & relationships

My friend and I always mess around with each other, he’s my ex boyfriend but we only started having actual sex after we broke up a long time ago. I love him & I’d literally do anything for him. but he doesn’t love me back the way I do anymore, but we have sex whenever we can and we talk over the phone a lot. Anyways, whenever I give him a blowjob he’s fine, & always cums. But when we have sex he stops being hard right in the middle of everything. Keep in mind that we’re only teenagers. I asked my sister what I could do about it or what was happening, and she said that he was most likely stressed or nervous. He said he was nervous, is there anything to prevent that from happening?