moh going to new boyfriends cousins wedding instead of rehearsal

The reality of bridal parties/weddings in general, is that nobody will care as much as the bride does. Was she flaky before the boyfriend? Has she acted like this before? If she has, it sounds like you may have chosen her based on how much you value her without considering her reliability! I'm so sorry this is happening, I can't imagine feeling less important on an experience as important as a wedding.

Did you set expectations that you wanted the MOH to attend all events, and throw you a bachelorette party? If those expectations are never set, there are PLENTY of women (esp on WW) who firmly believe they only need to show up to your wedding. Period. If that was not the expectation you had, you definitely need(ed) to set it. If you never set any of these expectations, you can't fault her for not doing things she didn't know were of the utmost importance to you.

If I was you, I would get with the other bridesmaids and see if they're interested in doing a night out/ weekend out etc. She's already let you down, and there's nothing you can do about it now besides continue making your wedding experience the best you can! I'm sure your other girls will step up for you if you just reach out.

Agree with the above. I dealt with multiple bridesmaids missing multiple events for me, and at the end of the day you just have to be grateful for the ones that do show up and are caring and thoughtful towards you. When your wedding has passed, you’ll find that who showed up on the actual day will be the only thing that matters to you.
I personally did not set many expectations with my bridesmaids except to buy the dress, shoes, and show up on the day-of for hair and makeup at a specific time so there would be no delays. When it came to other things like decorating or planning, I put this expectation solely on myself and FH. A lot of brides on WW have posted about disappointment with bridesmaids not helping with planning or decorating, and the answer from many is always the same - don’t rely on or expect bridesmaids to assist with that. As far as the bachelorette, I see no problem bringing it up with the bridesmaids and asking if they would like to do something. You may find that one of your other bridesmaids will volunteer to host it.
I realize the rehearsal dinner is still a big event when it comes to weddings, and I’m sorry your MOH can’t come and support. I hope you’re able to get to a place mentally and emotionally where you can just focus on who’s there to support instead of who doesn’t show. Best wishes to you!

I am so so sorry she is doing this to you. It's very selfish and rude, and I understand the pain it's causing you. You are not being overly sensitive...she is being insensitive. I had something similar happen to me with my first wedding, and this time around I set zero expectations around any of my bridal party supporting me so I wouldn't get hurt again. I'm sorry

Sounds like it's a tough choice for her. If she's been with this boyfriend for a few months, then his cousins wedding may trump your rehearsal in her mind. She'll be there for what's important, your wedding day.

The true fact is that no-one will hold your wedding to the same level of importance that you and your spouse will. Focus on gratitude for the positive things, and the ways that people do show up for you.