This friend seems like a very important person in your life. Anyone who truly cares about you and wants to be with you should be able to understand this and respect it. It's going to be about explaining to your new love interest how you feel about this friendship and how you were both there for each other during difficult times in your life and that you will always be important to each other. my Girlfriend has two exes she is very good friends with and i have a couple of exes i still talk to and one is a good friend. Wwe are both able to respect each other's friendships with these people and jealousy has never been an issue. Wwe both explained how Wwe each feel about these people and why they are important and Wwe both know each others friends and get along with them both. If your new interest can't get over this issue and become comfortable with your friend then it's definitely a sign that it's not a good relationship match for you. i always disagree with letting go of important friendships, or any friendships because of a new relationship.
It's worth mentioning that this advice is valid only as long as your friend is respectful of your romantic relationship and not likely to try and drive a wedge between you and your new interest or be jealous of time you spend with a new partner or anything like that. i've been in some pretty nasty situations with past girlfriends where their friends, ironically usually friends who were never exes or romantic or sexual interests, work really hard to drive us apart because they're jealous that i'm now taking their friend's attention away from them. i think i've probably just had really bad luck in this area to have it happen multiple times because i don't honestly think it's that common, but it does happen so it warrants consideration.
Probably in order for it to work, they will need to get to know each other and at least be comfortable around one another. Good luck. Situations like this suck.