I hope all this time you have been correctly reporting this ebay business on sch C's etc
I personally am not in favor of forming an LLC in situations like yours, those become more complicated than you need to do at this time
if you form a partnership, this will require an EIN, you will file a 1065 and K(1)'s to each partner of their share of the profits, which in turn will be reported on your personal tax return on Sch C and SE
since you have a regular job, work out some kind of arrangement that your friend operate as a sole proprietor, working out some method of your share of the profits that can be claimed as and expense for them