Seen F.R.I.E.N.D.S? I'm sure you must have and if you haven't, well, we feel sorry for you. All of us fans have been waiting for our Chandler or Monica respectively. Their relationship had everything- friendship, trust, loyalty, understanding, acceptability and a whole lot of love. However, we are sorry to burst your fantasy bubble but even if you manage to find them(highly improbable), it's not going to last. There are way too many hurdles that such a relationship has to go through which were easily bypassed in the show. But in real life, the stakes are too high and sometimes not even worth it. You will always be on the verge of losing a best friend and that's not an easy loss to cope with.
First things first; the way their relationship started- they were friends with benefits with no romantic angle to it. It was a huge gamble, and no, "no risk, no gain" doesn't work everywhere, they might have just ended up losing everything.
If you decide not to go ahead with it anymore, there will nonetheless remain an awkward tension between you guys.
One of you might not feel the chemistry and then it would be plain awkward, you just can't forget that it happened. Just doing it with your best friend can screw up your entire relationship. What if it isn't good, what about the awkward next morning? You wouldn't know if they even want it anymore.
And if they don't, you may remain friends but it won't be the same anymore. Any mention of physical intimacy is going to make you both shuffle in your seats. You will have just lost a friend in front of whom making sexual jokes was totally appropriate up until now.
Both of you may not be on the same page, one might fall in love and the other might not.
Let's consider all goes good and you feel fortunate to have decided to do this. But let's not forget the issue of falling for them, it's really terrible when one person catches feelings and the other doesn't. We all have heard stories of FWBs gone wrong. It seemed beautiful in the show with Chandler declaring his love for Monica when she was acting all funny, but we all know how painful it is when you tell someone you love them but don't get to hear it back.
Friends aren't always as supportive as the ones in the show. Personal emotions can come in the way of being happy for you.
In the show, they lived next door and were lucky enough to be able to meet in secret like that. They had 3 amazing friends and one excessively supportive brother, but what if friends don't understand, how well do you think they are going to take it? When you try to hide something like this from your friends, it's not always easy. You will be missing the same get togethers and be unavailable at the same time. People take the hint eventually and then there can be a whole range of mixed reactions. You can't expect everyone to be supportive, some may even be jealous and take jibes at you.
Phoebe, Joey, and Rachel were non-judgemental when they were 'just doing it' and completely ecstatic when they declared their love for each other. Even Ross came around despite his anger issues.
You share different dynamics with a person as their friend and as a lover, the change might not be a pleasant one.
You might like someone a lot as a friend, but there may be a whole different side of them as a lover. You might find shortcomings in them that you never even thought of before. There are things that don't bother you about someone when you are just a friend but can be an issue when you are introducing them to the world as your partner. In the show, Monica handled Chandler's awkwardness pretty well and he, her dominating nature.
Also, you might share different dynamics with someone when they are your friend as compared to your lover. They might be sensitive or aloof or clingy as a lover and you might just not like it.
Breaking up with them is one of the biggest issues. Not always do you get to walk the aisle with your best friend cum lover. Your break-up might just split your whole group like it happened when Ross and Rachel broke up. People will be reduced to taking sides, there will be just a whole lot of unnecessary drama.
You will feel the pain of having lost a close friend and wish you had stuck to just being friends.
This break up can hurt you worse than breaking up with a stranger because you will begin questioning your entire friendship with them, even the good times. Your friends are inevitably going to ridicule you guys or proclaim to have serious insight like they knew it wasn't a good idea in the first place and you might just end up losing your shit on them, making you even more lonely than you already are.
No matter how badly we want it to be, reality is hardly ever as beautiful as in the show. Having someone who loves you like Chandler did or stands by you as Monica is really great and we hope that you find that someone sooner rather than later, but having a similar love story isn't really a good idea. Because if it goes good, it will be great, but if it goes bad, it will be awful.