I'm uncertain about wanting to be in a relationship right now.

I’m an 18-year-old woman in a relationship with my boyfriend, who is 19, for nearly three months now. For anonymity, I’ll refer to him as "Mark." We connected through a dating app, and I believe our relationship is generally happy and healthy. However, I'm starting to question whether I want to be in a relationship at all. Mark is very sensitive, which can be challenging for me since I'm battling my own emotions and he often seeks reassurance that I’m not sure I can provide. On top of that, my sexual needs are quite significant, and I've noticed that Mark's feelings about intimacy have shifted since we began dating. I'm still young and eager to explore experiences like threesomes; in fact, I've never even kissed a woman, but I'm keen to try at least once. When we first started dating, I made my intentions clear, and he expressed interest in exploring those options. Lately, however, he’s decided against it, claiming that his feelings for me make sharing difficult. Mark is also relatively inexperienced when it comes to sex. Although he sees himself as dominant and I take on a submissive role, he often seems insecure and hesitant to explore new things. I’m realizing there are many sexual experiences that I doubt he’ll ever want or be able to provide. Putting all of this into words makes me feel guilty, as I do care for him, and I know he cares for me too. Yet I’m uncertain about how to navigate this situation and would greatly appreciate any insights or advice. I’m open to answering any questions for further clarity.