How to maintain your friendship, when a third person joins the circle
You should understand that by default, your relationship dynamics with your friend may change after a romantic relationship, marriage, business partnership, etc. enters into your friend's life. This can leave little space for you as a closest friend. Normally the change is brief and things will settle after some time, so during this temporary change in relationship dynamic, you can make use some of these suggestions.
1. Continue acting like you are friends
Continue acting like you're friends. Converse with them frequently, be friendly, polite and caring, share a laugh, yet don't force the issue or bring about unnecessary drama, don’t give them any more reasons not to want to spend time with you, don't choke them with too much attention, but also don't over stay way, you don't want your friend to start considering the fact that you have found other friends, that would be disastrous.
2. Don’t be too clingy
Try not to be clingy. Friends are like an elastic band: one moment they are there for you, and afterward they extend away however under normal circumstances, given the time and space, they will surely come back to you. if you under any circumstance allow them to have the impression that they are not permitted to have other individuals in their life, they'll push much harder to get away from you and your endeavors to control them.
3. Make new friends of your own
Make new friends you could call your own. For one thing, making friends – even just hi friends – will bring back your confidence and am sure you likely need a lot of it at the moment, it also helps take your mind of your friend. On top of that, it will remind your friend that you have a life of your own and that, if they really want and cherish your friendship, they need to put in extra effort to keep the friendship going. And also, it will remind your other friend that you're a fun individual with something to offer.
It is of utmost importance that you do this with the right attitude and mentality. if you do it just to spite or get back at your friend, it will be obvious to them, make you look childish, and this is going to drive your friend more away from you, and, to top it all off, make your new (supposed) friends feel objectified and used. if you can actually make a new friend just to spite an old friend, then that is enough justification to make any friend leave you
4. Keep an open mind with the new friend
Connect with your friend's new friend. Possibly you are ignoring them just because you are jealous and envious of them when, truly, they're really cool. Keep an open mind and attempt to become friendlier with the new friend by inviting both them and your friend out to something. (If you anticipate there's a probability you'll wind up being the awkward extra person, invite someone else or two to be safe.) In the event that it’s another boyfriend or girlfriend, be excited for your friend's happiness and give them a chance to feel like they can trust in you.
5. Relax, It will soon be over
Let's be honest: new relationships and friendship come and go pretty quickly. And if you and your friend have been good friends for quite a while, the change is probably temporary, particularly if it’s a boyfriend or girlfriend issue you're dealing with. Truth be told, you're most likely the first person your friend will come crying to when everything blows over, so try to have a great time and develop new friendships during this period. When it’s over, ideally your friend will remember why you're a keeper, and they will be back.
Important things to note
Stay in contact with them and remind them that they're your closest friend, then they will feel terrible about overlooking you, and this will make them come back to you
Never, ever set out purposefully to make them jealous. Joining another click, snickering and chatting with the new click and after that laughing at your previous friend won't solve things. It will only make the situation worse.
Never sound angry or jealous when confronting your friend.
Being truly mean to your friends' new friend or boyfriend/girlfriend will just make your friend support them against you and this will start a conflict, trust me you don't want this to happen