18 year old who has been in a relationship for just over a month (first ever)

Hello fellow wankers my name is Martin. So I wank everyday, probably 2-4 times a day. I recently got a great girlfriend who is up for anything. She has given me a number of blowjobs but we haven't had sex yet. I did insert my penis into her vagina earlier on in the week but I kept going soft. I'm not sure whether it's because she kept teasing me so much that night (almost having an orgasm and stopping) or there's something wrong. I almost cummed from sex but then she stopped because her mum was nosying about. We tried again about 20 minutes later but I went completely soft and couldn't get hard again. Is teasing too much for a virgin like me? Also I agreed I wouldn't wank in till I next see her, lets just say that has failed big time. I want to stop wanking completely and save all the juice for her but I'm not sure whether I will be able to.