Why does masterbating ruin sex?

Hii! Ok so I’m a 18 year old female who is sexually active with my partner that I’ve been with for 3 years. He lives a little far away from me so we see eachother every 2weeks-1month 🤷🏽‍♀️ and every time I see him the first day we engage in sexual intercourse.

I always look forward to it because it’s a little time that’s just special for us.

Anyway, recently I’ve noticed that if I go the whole month without masturbating and then I have sex with him it feels like best thing ever. BUTTT, if I do masturbate during that space of time it just doesn’t feel as great.

I feel like it’s normal but Is it common?