This doesn't look like past tense to me, it reads since to you go in my mind!
It's just how the construction is formed in Welsh with ers. It doesn't look like the past tenses you've learnt but it is translated as one in English.
Diolch yn fawr am y wybodaeth diddorol!
Is this "since" closer to because or after?
"Since" as in time, not because.
PS How do you do bold on the comments here?
And for good measure, `yellow, constant-width text that ignores the meaning of asterisks` = yellow ... asterisks
`yellow, constant-width text that ignores the meaning of asterisks`
yellow ... asterisks
Diolch i ti!
, dw i'n gallu anadlu am y tro cyntaf!
Our guests all bring happiness: some when they come, and some when they go.
That sounds like something my late father-in-law used to say, picked up from an older relative - "It doesn't matter how sad we are when you arrive, we're always happy when you go."
"I hate when she leaves, but I love to watch her go."
Probably a coincidence, but erst (as in erstwhile) is a wonderful mnemonic for ers.
Why not "since you have gone" .. "since you went"
That should be right too.