Based on the information you provided, it's possible that you may have misread the situation. When someone is flirting with you intensely, it can be confusing and lead to mixed signals, especially if they are already in a committed relationship.
Here are a few possible explanations for his response and subsequent behavior:
He's in a Relationship: His adamant response of "no" suggests that he is currently in a relationship and not available to pursue anything beyond friendship. Flirting, even if it seemed intense, doesn't necessarily mean he's looking to start a romantic relationship with you.
Feeling Awkward or Guilty: After answering, he may have felt awkward or guilty about his behavior, leading him to distance himself momentarily by checking his phone.
Just Flirting for Fun: Some people enjoy flirting for the thrill of it without any intention of taking things further. It's possible he was simply flirting for fun or to boost his own ego.
Misinterpretation: It's also possible that he is single, but his response was misinterpreted due to nerves or an unintentional misunderstanding.
Regardless of the reason for his response, it's important to respect his words and boundaries. If he is indeed in a relationship, it's best to maintain a friendly but platonic relationship with him. If you feel uncomfortable or uncertain about the situation, it's okay to take a step back and prioritize your own feelings and well-being.
If he continues to flirt or if you feel that his actions are making you uncomfortable, consider communicating your feelings honestly and openly with him. Setting boundaries and being clear about your expectations can help establish a healthy dynamic in any relationship, whether it's romantic or platonic.