My Boyfriend And I Have Been Making Out And Each

My boyfriend and I have been making out and each time I sit on his lap. He always has an erection and my underwear is always wet from getting "turned on". I have masturbated a few times when I have gotten home and he touches me down there (with pants on). I don't think he has ejaculated while we've done this (I think I would've noticed) but I am worried that I could possibly get pregnant from this. Could I? Please help.