Help! My fiancé is a people pleaser & now we have invite trouble

Perhaps hit him with the per head cost of your wedding and explain that adding people adds to the bottom line? Also, will your venue fit all of these extra people? (Remember that you can only have as many as the fire code allows, and that number includes the two of you and any vendors.)

Don't send anything yet - not even STDs, since that's a "soft" invitation - at least not until you get it sorted.

You can have him make a list of everyone he wants to invite, and have them listed as Must Invite to Want to invite. From there, however many you have allocated per side (i'm going to use 30 for example). Tell him that the first 30 listed will be the ones invited. If he sees that 31 is someone he wants invited, then he will need to pick one from the original 30 to take their place. Or every extra person he wants to invite consider him paying for them/having a way to pay for them before invites go out. I'm assuming you've had the budget talk with him, but it doesn't seem like it's registering or he is just trying to wing it and hope that you will cave. If yall can't afford it, the money won't just pop out of thin air

Has he seen how much everything costs? I have an excel spreadsheet that is calculating every line item
As I enter it. Guest count affects everything. The less guests you have will minimize everything else such as invitations, decor, welcome bags, etc. Show him the projected grand total, as it may change his thinking.
I know my total is larger than I thought.

Try another approach and say you really want your sides to be as even as possible because you don't want to feel lonely at your own wedding. People understand their is a spouse/ co-host.

Depending on your comfort level, I would figure out the number of attendees you’re comfortable with at your budget, and for every person over that he wants to invite, ask that he contribute financially to cover the cost if they RSVP yes. I think the bride and groom can invite whomever they want to the wedding, but each should understand the financial impact that each “yes” has and each person’s limits on what they are comfortable with / willing to contribute. If he pays for their cost, would you mind them attending?

#1 reminder: the wedding is about both of you! It's not about impressing or pleasing anyone else. Some of the invitees will come and go in your lives. Decide which ones you think will always be there and who will just be there because it's a potential party or they want to be a one-upper themselves. The latter are those I think you wouldn't care if they attend or not. You can extend/invite them but don't plan your day around them being there. The wedding couple ultimately calls the shots - others can stay home if they have motives. OR invite them and only plan for a certain capacity number and if you run out food or whatever, it is what it is and brush it off. The event will happen and be over with sooner than you realize, and you'll wonder why you worried about some things in the end.

Is he paying for these people? Who is paying the bulk of the costs for the wedding? If it’s no him, then I would say that if he wants to pay for them (within venue limits) then he can invite them?

You have two options: you can invite everyone and serve cake and coffee only as was popular in parents’ and grandparents’ generations. Or you can cut the list to only your nearest and dearest current social circle and host get togethers for the other groups throughout the year. Send announcements to those who don’t make the invite list. Contrary to popular belief, your wedding is not the only party you will host as a married couple in your entire lifetime. Have bbqs or game nights with friends, a different group each time. Start an annual tradition of a family reunion picnic at a local park facility that people can either potluck or have an inexpensive local restaurant deliver drop off catering. Get together on a regular basis with family and friends: friendsgiving, a backyard picnic, a Christmas cookie exchange, the list goes on.

What about your venue? What’s the max number of people that the ceremony and reception area will allow? Maybe that will help decrease the # of guests.
You’ll also have to explain to him the cost per person as everyone has stated and the total cost if he wants to invite everyone. Big weddings was a thing in the past where you invite everyone and their moms. With covid, it’s has changed the vibe of weddings making it more intimate. So maybe play the covid card as well?