"I [21F] have been thinking about someone else while in relationship [21M]"

I 21F have been with my boyfriend 21M for two years, but lately I’ve been thinking he isn’t the person I want to marry. His sarcasm and constant wanting to bicker leaves me feeling frustrated and I don’t want to feel this way for the rest of my life. I do love for him, but I worry we have just grown into different people. I have thought about talking through my feelings with him so we maintain transparency and honesty in our relationship, but conversations like this end with him crying, begging