Is a trip to USA for 49 days to see gf too long? [closed]

Write a letter like this, with your name, address, and phone number at the top:

To whom it may concern:
I am an American citizen. boyfriend's name will be staying as a guest in my home for the dates of start-date to end-date, after which he will be returning to the UK to resume working with work-provider.
Signed: your name

And have your boyfriend's work-provider sign a letter like this, with their name, address, and phone number at the top, and some details about the work-provider's line of business (including a website, if they have one):

To whom it may concern:
boyfriend's name has been working for me on a contractual basis since whenever, and he will be working for me again from some date shortly after his return.

Your boyfriend can show these to immigration when he lands. Make sure you are contactable by phone when your boyfriend arrives in the US. If possible, ask the work-provider to be contactable at the same time.

Edited to add: As jcaron points out in the comments, your boyfriend should only show these to the immigration officer if he is asked. And he should certainly have a return plane ticket that he can show if asked.

From personal experience I've stayed for the full VWP days to see my girlfriend when she lived in the States. I also went a few times for less amounts of time (1-2 weeks)

You get a bit more questioning but if you're honest you're fine. Having some connection like a job or uni to go back to helps. I didn't many ties to go back to as I'd just finished college, apart from family when I went for 3 months so the IO was pretty aggressive with the questioning which is understandable, but I just answered everything honestly. Make sure the return flights are booked.

I never used a letter like TonyK says but it may help.

Just make sure he doesn't lie, the truth always comes out and could make him illegible for the VWP in future.