“Take all my loves, my love, yea take them all”
The word 'love' carries two meanings simultaneously throughout the opening quatrain: the persons the speaker loves (including the mistress) and the feeling of love itself. Line 547 opens with a triple pun — 'all my loves' (all the people I love), 'my love' (you, the addressee), and the capacity for love the speaker has already given over — so that the Youth taking 'all my loves' turns out to be taking nothing new, since line 550 adds 'All mine was thine, before thou hadst this more.'
historical The Fair Youth, the Dark Lady, and the Rival Poet“if thou thy self deceivest By wilful taste of what thyself refusest”
'Wilful' means deliberate, chosen with full knowledge — not accidental or forced. 'Taste' here means indulgence or experience. The line accuses the Youth of knowingly enjoying something he has already forsworn (presumably a vow of faithful friendship), which makes him guilty not just of taking the mistress but of deceiving himself about his own character.
“love knows it is a greater grief To bear love's wrong, than hate's known injury”
The couplet before the final couplet states the sonnet's emotional core as an axiom: it is harder to bear an injury from someone you love than a comparable injury from an enemy. A stranger's cruelty is predictable ('hate's known injury' — you expect it from a known enemy); a beloved's betrayal is worse because it comes from inside the bond of trust. 'Love knows' invokes love itself as a witness, almost a judge.