Marriage is a commitment that should best be viewed from a long term perspective, rather than giving into impulses. While passion is an important aspect of a healthy romantic relationship, it is also time bound and likely to gradually fade away. What matters more as time goes by is compatibility, intimacy and a sense of commitment. When deciding on whom to marry, also consider your own sense of comfort and trust with your partner.
At the end of the day, which of these men you want to marry is a call that only you can make, but consider all the aspects of your relationship with both of them before you make your decision. At the same time, if you feel like this other guy pursuing you is making you feel uncomfortable, it would be a good idea to express your discomfort to him and ask him to stop doing so in the future.