I wonder if perhaps Marvell is adopting a slight tone of irony?
To refer to despair as 'Magnanimous', in 'show[ing] me so divine a thing', despite the fact that to this within range of this thing 'feeble hope could ne'er have flown' is surely disingenuous, I would suggest in an intentionally ironic way.
If we then consider Marvell's 'conclusion', that love is 'the conjunction of the mind,/ And opposition of the stars', perhaps this gathers greater weight? Clearly the intention of any Philosophical explanation is exposure, and this is borne out by the structure/lexis of the poem 'And', 'For', 'Therefore', as stanza starters. Thus, Marvell's ambiguous, and totally useless, definition seems to contradict the general structure and purpose of such a logical exposition.
Perhaps, then, we could also detect irony in Marvell's portrayal of love between those who 'can never meet' as 'infinite' in contrast to that of those who, 'in every angle greet'. To some extent it seems strange to suggest that a love which never comes to fruition in the physical sense is 'infinite'. Moreso if the suggestion is that the two would never even become aware of each other. However, I'm sceptical of the validity of this analysis, for it's true that the penultimate stanza concurs with neo-platonic Philosophy, and this could quite likely have been Marvell's aim.