[Evisse the Blue]

So maybe Morgoth lusted for the silmarils exactly because they encompassed the pure and good ("light") that he was so afraid of. He wanted to corrupt that which was most precious to the good ones and most dangerous to him, therefore scoring a 'double victory': deprive the Valar and Elves of the light and confront his own fear in the process. Corrupting and ruling over the thing he feared and hated the most gave him a 'satisfaction' as similar to 'love' as he could get. Because he was technically 'unable' to feel 'love' - in the true sense of that word, so when we speak of love in relation to Morgoth and Ungoliant we mean lust, or a base satisfaction.

As for poor Gollum, (and Frodo. to some extent), it was a different story. Mark12_30's addiction idea comes close to explaining it, but it's so weird, because even when the Ring was in their possession, they felt no happier...Gollum was certainly miserable, hungry and grumpy even when he had the Ring, while poor Frodo had awful visions and felt helpless and terrified.