Is it possible that some changes are needed? (21F and 20M)

**TL;DR:** I need to come to terms with some boundaries in my relationship that feel off but aren't necessarily unusual. I (21M) and my partner (20M) have been together for nearly two years, and our relationship is generally good—no major fights, just the usual minor disagreements. However, I've noticed that our approach to sexual activity has become a bit uncomfortable for me. I enjoy being intimate with him, but I'm not always in the mood. When I don’t feel like it, he might express that he’s feeling horny or wants to be intimate. Instead of outright saying “no,” which feels odd given our relationship, I often say things like “I’m not sure” or “I’m tired.” Sometimes he continues to push for it. While he never physically forces anything, his actions—like touching himself if I turn away—make me feel pressured to respond, which can be difficult. It’s led me to want to avoid being alone with him, not because I'm afraid of him, but because I dislike how he sometimes persuades me into something I’m not sure I want to do. I'm unsure if this is a serious issue I need to address or just something that comes with being in a relationship.