There could be several reasons why your ex's friends are making suggestive advances towards you after you were friends with benefits (FWB) with him. Here are some possible explanations:
Curiosity: They might have heard about your previous relationship with their friend and are curious about what it was like. They might be interested in exploring a similar dynamic with you.
Jealousy: Seeing you being intimate with their friend might have triggered jealousy or feelings of missing out, leading them to pursue you as well.
Competitive nature: Some people might see it as a challenge to "win you over" after you were involved with their friend, especially if they feel a sense of competition or rivalry within the friend group.
Opportunity: Being friends with benefits with your ex might have created an impression that you are open to casual relationships, making them feel more comfortable approaching you for the same reason.
Lack of boundaries: Some individuals might not respect boundaries and might see your previous relationship with their friend as an opportunity to pursue you without considering the potential consequences.
Testing the waters: They might be testing to see if you are open to dating someone else within the same social circle or friend group.
Regardless of the reasons, it's essential to prioritize your own feelings and well-being. If you're not interested in any further intimate involvement with your ex's friends, it's crucial to communicate your boundaries clearly and assertively. Let them know that you are not interested in pursuing anything beyond friendship. If they persist or make you uncomfortable, it might be a good idea to distance yourself from those individuals and evaluate the nature of your relationship with your ex as well.